Low dielectric constant (low-k) materials are developed to meet the ever increasing challenges in the IC industry in terms of RC delay. These low-k materials are typically highly porous in order to decrease the k value. For porous dielectric films to meet the standards for integration into the next generation microelectronic devices, the pores are preferably sealed to prevent diffusion of metal ions, water and chemical precursors from barrier and seed deposition steps, such as etching and chemical mechanical planarization.
In Y. Sun et al. (Solid State Phenom. 195, 146 (2013)), a novel pore sealing approach is described wherein a self-assembled monolayer (SAM) is deposited on a porous substrate, followed by the deposition of a thin TiN layer. Before the SAM layer deposition, the dielectric surface needed to be modified/activated in order to make it more reactive toward the sealing layer. This was performed by the introduction of hydroxyl groups via a plasma treatment. However, the used plasma technique showed poor selectivity toward the surface versus the bulk of the film (FIG. 1), meaning that the film was also modified in its bulk. As a consequence, the SAM molecules were not only deposited on the surface but also inside the pores in the sub-surface region, which resulted in a significant increase in the k-value of the dielectric film.